The present invention generally relates to regulators and, more particularly, to apparatus and methods for measuring operational parameters across a regulator and calculating flow.
In the control of fluid in industrial processes, such as oil and gas pipeline systems, chemical processes, etc., it is often necessary to reduce and control the pressure of a fluid. Regulators are typically used for these tasks by providing adjustable flow restriction through the regulator. The purpose of the regulator in a given application may be to control flow rate or other process variables, but the restriction inherently induces a pressure reduction as a by-product of its flow control function.
By way of example, a specific application in which regulators are used is the distribution and transmission of natural gas. A natural gas distribution system typically includes a piping network extending from a natural gas field to one or more consumers. In order to transfer large volumes of gas, the gas is compressed to an elevated pressure. As the gas nears the distribution grid and, ultimately, the consumers, the pressure of the gas is reduced at pressure reducing stations. The pressure reducing stations typically use regulators to reduce gas pressure.
It is important for natural gas distribution systems to be capable of providing sufficient volumes of gas to the consumers. The capacity of this system is typically determined by the system pressure, piping size, and the regulators, and system capacity is often evaluated using a simulation model. The accuracy of the system model is determined using flow data at various input points, pressure reducing points, and output points. The pressure reducing points significantly impact the capacity of the gas distribution system, and therefore it is important for the system model to accurately simulate the pressure reducing points. The pressure reducing points, however, are within the distribution system and therefore are not considered custody transfer points (i.e., points at which the control of gas flow switches from the distribution system to the consumer). As a result, flow measurement is typically not provided at the pressure reducing points. Furthermore, since the pressure reducing points are not custody transfer points, the added cost of high accuracy is not required. Flow measurement problems similar to those described above with respect to natural gas distribution are also present in other regulator applications (i.e., industrial processes, chemical processes, etc.).
In addition, regulators are subject to failure due to wear during operation, thereby reducing the ability to control pressure along a pipeline. A damaged regulator may allow fluid to leak, thereby increasing fluid waste and possibly creating a hazardous situation. While damaged regulators may be repaired or replaced, it is often difficult to detect when a regulator has failed and determine which regulator is damaged. Detecting a failure and determining which regulator has failed is more difficult in a typical natural gas delivery system, where pipelines may run several miles. Accordingly, apparatus which detects apparatus failure and identifies the location of the failure is greatly desired.
In accordance with certain aspects of the present invention, apparatus is provided for determining fluid flow through a pressure regulator disposed in a fluid flow passage, the pressure regulator including a throttling element moveable in the flow passage. The apparatus comprises a first pressure sensor in fluid communication upstream of the throttling element for measuring an upstream pressure P1, a second pressure sensor in fluid communication downstream of the throttling element for measuring a downstream pressure P2, and a travel indicator for determining a throttling element position Y. A processor is associated with the first pressure sensor, second pressure sensor, and travel sensor, the processor having a stored program for determining a flow rate F based on the upstream pressure P1, the downstream pressure P2, and the throttling element position Y.
In accordance with additional aspects of the present invention, a method is provided for determining fluid flow through a pressure regulator disposed in a fluid flow passage, the pressure regulator having a throttling element moveable in the flow passage. The method comprises the steps of generating an upstream pressure value P1 by measuring fluid pressure upstream of the throttling element, generating a downstream pressure value P2 by measuring fluid pressure downstream of the throttling element, and generating a travel value Y by determining a position of the throttling element. A fluid flow value F is calculated based on the upstream pressure value P1, downstream pressure value P2, and travel value Y.